Contactless power reception device and reception method

ABSTRACT

A wireless power reception device and a wireless communication method thereby are provided. The wireless communication method by the wireless power reception device may comprise the steps of: receiving a wireless power signal from a wireless power transmission device; measuring the strength of the wireless power signal; modulating the amplitude of the wireless power signal according to the measured strength of the wireless power signal; and performing communication with the wireless power transmission device by using the signal having the amplitude modulated.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2015/005252, filed on May 26, 2015, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 62/002,942,filed on May 26, 2014, all of which are hereby expressly incorporated byreference into the present application.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless charging, and moreparticularly, to a contactless power reception device.

Related Art

In recent years, supply of portable electronic devices including a smartphone, a laptop, an MPEG-1 audio layer (MP3) player, a headset, and thelike has been spread. However, since the portable electronic devicesoperate by consuming power stored in battery cells (e.g., a primarycell, a secondary cell, and the like), the battery cell needs to becharged or replaced in order to continuously operate the portableelectronic devices.

A method of charging the battery cell is generally divided into acontact type charging method of charging the battery cell by using apower supply line and a power supply terminal and a contactless chargingmethod of charging the battery cell with wireless power induced by amagnetic field generated from a primary coil of a wireless powertransmitting apparatus by using a wireless power reception device.However, in the contact type charging method, an instant dischargephenomenon occurs as different potential differences are generated atboth terminals when a charger and a battery are coupled to or separatedfrom each other and the power supply terminal is exposed to the outside,and as a result, fire may occur when foreign materials are accumulatedin the power supply terminal and the battery is naturally discharged andthe life-span and the performance of the battery deteriorate due tomoisture. Accordingly, in recent years, in order to solve the problems,a research into the contactless charging method has been in activeprogress.

As one of technologies associated with the contactless charging method,“Contactless Charging System” of Korean Patent Registration No.10-0971705 discloses that a wireless power signal is transmitted bydetermining measuring a delay time up to a time of receiving a responsesignal corresponding to a request signal from a time of outputting therequest signal through a primary-side core unit and comparing themeasured delay time with a reference stand-by time when a load change issensed in the primary-side core unit of a contactless power transmissiondevice and thereafter, determining that a corresponding object is aforeign material when the measured time is shorter than the referencestand-by time and determining that the corresponding object is a normalcontactless power reception device when the measured time is longer thanthe reference stand-by time.

In the magnetic induction type contactless charging system, the wirelesspower reception device generally communicates with the wireless powertransmission device by an amplitude-shift keying (ASK) modulationmethod. In detail, when the amplitude of the wireless power signal whichthe wireless power reception device receives from the wireless powertransmission device is modulated, the modulated signal is induced to atransmitting coil of the wireless power transmission device. Thewireless power transmission device performs communication by detectingthe modulated signal induced to the transmitting coil. However, in thecontactless charging system, as the intensity of the wireless powersignal transmitted from the wireless power transmitting apparatusincreases, distortion occurs in the modulated signal and this causes acommunication error between the wireless power transmitting apparatusand the wireless power receiving apparatus.

SUMMARY OF THE INVENTION

The present invention provides a wireless power reception device whichcan smoothly communicate with a wireless power transmission device evenwhen the strength of wireless power transmitted from the wireless powertransmission device increases in a contactless charging system.

The present invention also provides a wireless communication methodwhich enables a wireless power reception device and a wireless powertransmission device to smoothly communicate with each other even whenthe strength of wireless power transmitted from the wireless powertransmission device increases in a contactless charging system.

In an aspect, a wireless communication method by a wireless powerreception device is provided. The wireless power reception deviceincludes: receiving a wireless power signal from a wireless powertransmission device; measuring the strength of the wireless powersignal; modulating the amplitude of the wireless power signal accordingto the measured strength of the wireless power signal; and performingcommunication with the wireless power transmission device by using thesignal having the amplitude modulated, and the modulating of theamplitude of the wireless power signal may be performed by a modulatorincluded in the wireless power reception device according to themeasured strength of the wireless power signal and the modulator may beimplemented to include at least one resistor and at least onetransistor.

The at least one transistor may be implemented by a metal oxide siliconfield effect transistor (MOSFET).

The modulator may be implemented to be configured in a direct current(DC) terminal of the wireless power reception device.

The modulator may be implemented to be configured in an alternatingcurrent (AC) terminal of the wireless power reception device.

The modulator may be implemented to include two or more transistors andtwo or more resistors.

In another aspect of the present invention, a wireless power receptiondevice is provided. The wireless power reception device includes: atleast one secondary core receiving a wireless power signal transmittedfrom a wireless power transmission device; a rectifier rectifying thereceived wireless power signal; a detection circuit measuring thestrength of the wireless power signal by monitoring an output of therectifier a plurality of modulators modulating the amplitude of thewireless power signal; and a controller controlling communication withthe wireless power transmission device by using the signal having theamplitude modulated by the modulator, and the modulator may beimplemented to include at least one resistor and at least onetransistor.

The at least one transistor may be implemented by a metal oxide siliconfield effect transistor (MOSFET).

The modulator may be implemented to be configured in a direct current(DC) terminal of the wireless power reception device.

The modulator may be implemented to be configured in an alternatingcurrent (AC) terminal of the wireless power reception device.

The modulator may be implemented to include two or more transistors andtwo or more resistors.

According to the present invention, since a wireless power receptiondevice modulates the amplitude of a wireless power signal according tothe strength of the wireless power signal transmitted from a wirelesspower transmission device to prevent a modulated signal from beingdistorted, smooth wireless communication is available even when strongwireless power signal are transmitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a contactless charging system accordingto the present invention.

FIG. 2 is a block diagram illustrating a wireless power transmissiondevice included in the contactless charging system.

FIG. 3 is a circuit diagram illustrating a wireless power receptiondevice included in the contactless charging system.

FIG. 4 is a block diagram illustrating a wireless power reception deviceaccording to an embodiment of the present invention.

FIG. 5 is a circuit diagram illustrating the wireless power receptiondevice according to the embodiment of the present invention.

FIG. 6 is a block diagram illustrating a wireless power reception deviceaccording to another embodiment of the present invention.

FIG. 7 is a circuit diagram illustrating the wireless power receptiondevice according to the embodiment of FIG. 6.

FIG. 8 is a block diagram illustrating a wireless power reception deviceaccording to yet another embodiment of the present invention.

FIG. 9 is a circuit diagram illustrating the wireless power receptiondevice according to the embodiment of FIG. 8.

FIG. 10 is a flowchart illustrating a wireless communication method of awireless power reception device according to an embodiment of thepresent invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsof the invention are shown. As those skilled in the art would realize,the described embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention. Inaddition, the drawings and description are to be regarded asillustrative in nature and not restrictive. Like reference numeralsdesignate like elements throughout the specification.

Throughout the specification, unless explicitly described to thecontrary, the word “comprise” and variations such as “comprises” or“comprising”, will be understood to imply the inclusion of statedelements but not the exclusion of any other elements. In addition, termsincluding “unit”, and the like disclosed in the specification mean aunit that processes at least one function or operation and this may beimplemented by hardware or software or a combination of hardware andsoftware.

A term called “wireless power” used in the present specification meanspredetermined type of energy associated with an electric field, amagnetic field, an electromagnetic field, and the like transmitted froma transmitter to a receiver without using physical electromagneticconductors. The wireless power may be called a power signal or awireless power signal and mean an oscillating magnetic flux enclosed bya primary coil at a transmitting side and a secondary coil at areceiving side. Hereinafter, a wireless power receiving apparatus and awireless communication method in a contactless charging system forwirelessly charging devices including a mobile phone, a cordless phone,a smart phone, an MP3 player, a laptop, a headset, and the like will bedescribed as an example. A fundamental principle of wireless powertransmission includes both a magnetic induction coupling method and amagnetic resonance coupling (that is, resonance induction) method usingfrequencies less than 30 MHz. However, various frequencies includingfrequencies at which a license-exemption operation is permitted atcomparative higher radiation levels, for example, less than 135 kHz (LF)or 13.56 MHz (HF) may be used.

FIG. 1 is a diagram illustrating a contactless charging system accordingto the present invention.

Referring to FIG. 1, the contactless charging system 100 includes awireless power transmission device 110 and one or more wireless powerreception devices 150-1 to 150-n (herein, n is a natural number).

The wireless power transmission device 110 includes a primary core. Theprimary coil may include at least one primary coil. The wireless powertransmission device 110 may have a predetermined appropriate shape, butone preferred embodiment may be a flat platform having a powertransmission surface. The respective wireless power reception devices150-1 to 150-n are positioned on the platform or near the platform toreceive wireless power from the wireless power transmission device 110.

The respective wireless power reception devices 150-1 to 150-n may beseparated from the wireless power transmission device 110. When therespective wireless power reception devices 150-1 to 150-n arepositioned near the wireless power transmission device 110, therespective wireless power reception devices 150-1 to 150-n include thesecondary core coupled with an electromagnetic field generated by theprimary core of the wireless power transmission device 110. Thesecondary core may include one or more secondary coils.

The wireless power transmission device 110 transmits power to thewireless power reception devices 150-1 to 150-n without a directcontact. In this case, the primary core and the secondary core aremagnetic induction coupled or magnetic resonance coupled to each other.The primary coil or the secondary coil may have predeterminedappropriate shapes. As one example, the primary coil and the secondarycoil may be copper wires wound around a high magnetic permeabilityformation such as ferrite or an amorphous material, but are not limitedthereto.

The wireless power reception devices 150-1 to 150-n are connected withexternal load (not illustrated, also referred to as an actual load ofthe wireless power reception device) to supply the power wirelesslyreceived from the wireless power transmission device 110 to the externalload. For example, each of the wireless power reception devices 150-1 to150-n may transport the received power to an object which consumes orstores the power, such as a portable electric or electronic device or arechargeable battery cell or battery

FIG. 2 is a block diagram illustrating a wireless power transmissiondevice included in the contactless charging system. Hereinafter, thewireless power transmission device will be described in more detail withreference to FIG. 2.

The wireless power transmission device 200 may include a primary core210, an electric driving circuit 220, a controller 230, and a currentmeasurement circuit 240.

The primary core 210 transmits a signal for detecting the wireless powerreceiving apparatus and a wireless power signal.

The electric driving circuit 220 is connected to the primary core 210 toapply electric driving signals to the primary core so that theelectromagnetic field is generated in the primary core 210.

The controller 230 is connected to the electric driving circuit 220 togenerate a control signal 231 to control an alternating current (AC)signal required when the primary core 210 generates an inductionmagnetic field or causes magnetic resonance. The controller 230 maycontrol an operation frequency, and voltage, current, and/or a dutycycle in the wireless power transmission device 200 according to a powercontrol signal received from the wireless power reception device.

The current measurement circuit 240 measures current that flows on theprimary core 220. The current measured by the current measurementcircuit 240 may be alternating current (AC). As one example, the currentmeasurement circuit 240 may be a current sensor. Alternatively, thecurrent measurement circuit 240 may be a transformer that lowers highcurrent that flows on the primary core 210 to low current and uses thelow current. Further, the current measured by the current measurementcircuit 240 may be direct current (DC).

The controller 230 may obtain information transmitted by the wirelesspower reception device by using a current or voltage value measured bythe current measurement circuit 240. The wireless power reception devicemay continuously or periodically transmit to the wireless powertransmission device 200 a power control signal to request an increase ofthe power or a power control signal to request a decrease of the poweruntil required power is satisfied by varying the load. When the wirelesspower transmission device 200 receives the power control signal torequest the increase of the power from the wireless power receptiondevice through the load variation, the wireless power transmissiondevice 200 decreases the power control signal to an appropriatemagnitude by using the transformer or a voltage distributor and performsenvelope detection by using a detector and thereafter, makes the powercontrol signal pass through a low-pass filter to detect the signal formthe wireless power reception device. In addition, the strength of thecurrent which flows on the primary core 210 may be increased so as totransmit higher power as a response to the power control signal. In moredetail, the controller 230 may adjust the control signal so as to applyan AC signal having a larger magnitude than a reference AC signal inorder to make higher current flow on the primary core 210. On thecontrary, when the controller 230 receives the power control signal torequest the decrease of the power from the wireless power receptiondevice, the controller 230 may adjust the control signal so as to applyan AC signal lower than the reference AC signal to the primary core 210so that power lower than the current transmission power is transmitted.

FIG. 3 is a circuit diagram illustrating a wireless power receptiondevice included in the contactless charging system. Hereinafter, astructure of the wireless power reception device will be described inmore detail with reference to FIG. 3.

The wireless power reception device 300 may include a secondary core310, a modulator 320, a controller 330, a rectifier 340, and a regulator350.

The secondary core 310 may be configured by at least one secondary coil.The secondary core 310 may receive a wireless power signal transmittedfrom the primary core of the wireless power transmission device.

The modulator 320 may be configured by an AC terminal of the wirelesspower reception device 300 as illustrated in FIG. 3 and modulate theamplitude of the wireless power signal received through the secondarycore 310. To this end, the modulator 320 may include a capacitor 321 anda transistor 322. For example, the modulator 320 turns on/off thetransistor 322 connected to the capacitor 321 to modulate the amplitudeof the wireless power signal received through the secondary core 310.The signal with the modulated amplitude may be induced to the primarycore of the wireless power transmission device through the secondarycore 310.

The controller 330 which is used for controlling an operation of thewireless power reception device 300 may control power supplied to a loadconnected to the wireless power reception device 300 as one example.Further, the controller 330 may perform communication with the wirelesspower transmission device by controlling the modulator 320.

The rectifier 340 may rectify AC power received by the secondary core310 to direct current (DC) power. The power rectified by the rectifier340 may be supplied to the load which is connected or mounted onto orincluded in the wireless power reception device 300. The rectifier 340may be implemented by a half-bridge, a full-bridge, or the like asillustrated in FIG. 3. In FIG. 3, as an example, it is illustrated thatthe rectifier 340 includes a plurality of diodes, but the diode of therectifier 340 may be replaced with the transistor such as a field effecttransistor (FET).

The regulator 350 is configured at a rear terminal of a bridge includinga plurality of diodes to supply the direct current (DC) power receivedthrough the bridge to the load connected or mounted onto or included inthe wireless power reception device 300. Herein, the bridge may serve toconvert input AC voltage to DC voltage and be implemented by thehalf-bridge, the full-bridge, or the like.

Meanwhile, although not illustrated in FIG. 3, the wireless powerreception device 300 may include a detection circuit which measuresstrength of the wireless power signal transmitted from the wirelesspower transmission device by monitoring an output of the rectifier 340.

When the strength of the wireless power signal detected from thedetection circuit is larger than or smaller than a predetermined controlpoint, the controller 330 may transmit information on power control sothat the wireless power signal with predetermined strength may bereceived by modulating the amplitude of the wireless power signalreceived from the wireless power reception device by means of themodulator 320. Alternatively, when the strength of the wireless powersignal detected from the detection circuit is beyond the predeterminedrange, the controller 330 may allow the strength of the wireless powersignal to be maintained within the predetermined range by modulating theamplitude of the wireless power signal received from the wireless powerreception device by means of the modulator 320. In this case, asillustrated in FIG. 3, when the capacitor 321 is used in the modulator320, constant impedance for a change in frequency is maintained, andthus even though the frequency is changed, the modulator 320 may performconstant amplitude modulation. However, when a resistor instead of thecapacitor 321 is used in the modulator 320, a response time may beminimized according to the used resistor, but since the impedance ischanged according to a frequency, when a full band is used, distortionaccording to the frequency may be caused. Further, even though thecapacitor 321 is used in the modulator 320, the magnitude of the powerreceived from the wireless power transmission device is larger than apredetermined value, the signal modulated by the modulator 320 may bedistorted. Since the distortion of the modulated signal causescommunication failure between the wireless power transmission device andthe wireless power reception device 300, the wireless power receptiondevice according to the present invention may include componentsdescribed below for smooth communication.

FIG. 4 is a block diagram illustrating a wireless power reception deviceaccording to an embodiment of the present invention and FIG. 5 is acircuit diagram illustrating the wireless power reception deviceaccording to the embodiment of the present invention. Hereinafter, thewireless power reception device according to the embodiment of thepresent invention will be described in detail with reference to FIGS. 4and 5.

First, referring to FIG. 4, a wireless power reception device 400according to an embodiment of the present invention may include asecondary core 410, a rectifier 420, a regulator 430, a detectioncircuit 440, a controller 450, and a modulator 460. The wireless powerreception device 400 is connected to an external load 470 to supplypower wirelessly received from the wireless power transmission device toa load 470.

The secondary core 410 may include at least one secondary coil receivingthe wireless power signal transmitted from the wireless powertransmission device.

The rectifier 420 may rectify AC power received by the secondary core410 to direct current (DC) power. The power rectified by the rectifier420 may be supplied to the load 470 which is connected or mounted ontoor included in the wireless power reception device 400. The rectifier420 may be implemented by a half-bridge, a full-bridge, or the like.

The regulator 430 is configured at a rear terminal of a bridge includinga plurality of diodes to supply direct current (DC) power receivedthrough the bridge to the load connected or mounted onto or included inthe wireless power reception device 300 through the regulator 430.Herein, the bridge may serve to convert input AC voltage to DC voltageand be implemented by the half-bridge, the full-bridge, or the like andthe regulator 430 converts the DC voltage of the rectifier into stableDC voltage and supplies the DC voltage to the load.

The detection circuit 440 monitors the DC voltage output from therectifier 420 in connected with the rear terminal of the rectifier 420to measure the strength of the wireless power signal transmitted fromthe wireless power transmission device.

The controller 450 may control communication with the wireless powertransmission device by using a signal with the amplitude modulated bythe modulator 460 based on the strength of the wireless power signalmeasured by the detection circuit 440.

The modulator 460 may modulate the amplitude of the wireless powersignal transmitted from the wireless power transmission device.

Hereinafter, the wireless power reception device of FIG. 4 will bedescribed in more detail with reference to the circuit diagram of FIG.5. In FIG. 5, as an example, a case where a secondary core 510 includesone secondary coil is illustrated. Referring to FIG. 5, a modulator 560is positioned between a rectifier 520 and using the plurality of diodesor FETs and a regulator 530 to modulate the DC power which is the outputof the rectifier 520. Further, the modulator 560 may include oneresistor 561 and one or more transistors 562 and 563. Since themodulator 560 includes the resistor 561, the response time may beminimized according to the used resistor. However, since the impedancevaries depending on the frequency, when the full band is used, thedistortion depending on the frequency may be caused, but since themodulator 560 is connected to the DC terminal of the diode bridge inseries as illustrated in FIG. 5, the modulator varies the current amountin the direction in which the signal flows to prevent the frequency frombeing distorted even with the high power. Further, the modulator 560 mayinclude a PNP transistor 563 and a controller 550 is connected to a baseterminal of the PNP transistor 563 to switch the modulator 560 andanaloguely control the magnitude of amplitude modulation according to aload change amount through the current control. Meanwhile, in FIG. 5, itis illustrated that the rectifier 520 includes a plurality of diodes,but the diode of the rectifier 520 may be replaced with the transistorsuch as a field effect transistor (FET).

Meanwhile, FIG. 6 is a block diagram illustrating a wireless powerreception device according to another embodiment of the presentinvention and FIG. 7 is a circuit diagram illustrating the wirelesspower reception device according to the embodiment of FIG. 6.Hereinafter, the wireless power reception device according to theembodiment will be described in detail with reference to FIGS. 6 and 7.

First, referring to FIG. 6, the wireless power reception device 600according to the embodiment of the present invention may include asecondary core 610, a rectifier 620, a regulator 630, a detectioncircuit 640, a controller 650, and a modulator 660. The wireless powerreception device 600 is connected to an external load 670 to supplypower wirelessly received from the wireless power transmission device tothe load 670.

The secondary core 610 may include at least one secondary coil receivingthe wireless power signal transmitted from the wireless powertransmission device.

The rectifier 620 may rectify AC power received by the secondary core610 to direct current (DC) power. The power rectified by the rectifier620 may be supplied to the load 670 which is connected or mounted ontoor included in the wireless power reception device 600. The rectifier620 may be implemented by a half-bridge, a full-bridge, or the like.

The regulator 630 is configured at a rear terminal of a bridge includinga plurality of diodes to supply the direct current (DC) received throughthe bridge to the load connected or mounted onto or included in thewireless power reception device 600. Herein, the bridge may serve toconvert input AC voltage to DC voltage and be implemented by thehalf-bridge, the full-bridge, or the like.

The detection circuit 640 monitors the DC voltage in connected with therear terminal of the rectifier 620 to measure the strength of thewireless power signal transmitted from the wireless power transmissiondevice.

The controller 650 may control communication with the wireless powertransmission device by using a signal with the amplitude modulated bythe modulator 660 based on the strength of the wireless power signalmeasured by the detection circuit 640.

The modulator 660 may modulate the amplitude of the wireless powersignal transmitted from the wireless power transmission device.

Hereinafter, the wireless power reception device of FIG. 6 will bedescribed in more detail with reference to the circuit diagram of FIG.7. A modulator 760 includes first and second modulation modules 765 and770. The modulator 760 is configured to be positioned between asecondary corer 710 and a rectifier using a plurality of diodes tomodulate AC power which is an output of the core 710. In this case, thefirst and second modulation modules 765 and 770 may include one or moreresistors 788 and 771 and one or more transistors 767 and 772,respectively. Since the modulator 760 includes the resistors 766 and771, a response time may be minimized according to the used resistors766 and 771. However, since the impedance varies depending on thefrequency, when a full band is used, distortion depending on thefrequency may be caused, but the response time and frequency modulationmay be more actively controlled by using two or more resistors 766 and771 and two or more transistors 767 and 772. The first and secondmodulation modules 765 and 770 may modulate the amplitude of thewireless power signal received through the secondary core 710 by turningon/off or analoguely controlling the transistor connected to theresistor. The signal with the modulated amplitude may be induced to theprimary core of the wireless power transmission device through thesecondary core 710. Further, the first and second modulation modules 765and 770 may include one or more PNP transistors 768 and 773 and acontroller 750 is connected to base terminals of respective PNPtransistors 768 and 773 included in the first and second modulationmodules 765 and 770 to control a current flow of the modulator 760.Accordingly, the modulator 760 is switched by the controller 750 and themagnitude of the amplitude modulation is analoguely controlled accordingto a load change amount through a current control to enable stablecommunication.

Meanwhile, FIG. 8 is a block diagram illustrating a wireless powerreception device according to yet another embodiment of the presentinvention and FIG. 9 is a circuit diagram illustrating the wirelesspower reception device according to the embodiment of the presentinvention. Hereinafter, the wireless power reception device according tothe embodiment will be described in detail with reference to FIGS. 8 and9.

First, referring to FIG. 8, the wireless power reception device 800according to the embodiment of the present invention may include asecondary core 810, a rectifier 820, a regulator 830, a detectioncircuit 840, a controller 850, and a modulator 860. The wireless powerreception device 800 is connected to an external load 870 to supplypower wirelessly received from the wireless power transmission device tothe load 870.

The secondary core 810 may include at least one secondary coil receivingthe wireless power signal transmitted from the wireless powertransmission device.

The rectifier 820 may rectify AC power received by the secondary core810 to direct current (DC) power. The power rectified by the rectifier820 may be supplied to the load 870 which is connected, installed, orincluded to the wireless power reception device 800 by the regulator830. The rectifier 820 may be implemented by a half-bridge, afull-bridge, or the like.

The regulator 830 is configured at a rear terminal of a bridge includinga plurality of diodes to supply the direct current (DC) power receivedthrough the bridge to the load connected or mounted onto or included inthe wireless power reception device 800. Herein, the bridge may serve toconvert input AC voltage to DC voltage and be implemented by thehalf-bridge, the full-bridge, or the like.

The detection circuit 840 monitors the DC voltage in connected with therear terminal of the rectifier 820 to measure the strength of thewireless power signal transmitted from the wireless power transmissiondevice.

The controller 850 may control communication with the wireless powertransmission device by using a signal with the amplitude modulated bythe modulator 860 based on the strength of the wireless power signalmeasured by the detection circuit 840.

The modulator 860 may modulate the amplitude of the wireless powersignal transmitted from the wireless power transmission device.

Hereinafter, the wireless power reception device of FIG. 9 will bedescribed in more detail with reference to the circuit diagram of FIG.9. Referring to FIG. 9, a modulator 960 may include two resistors 961and 962 and two transistors 963 and 964. The two transistors 963 and 964may be a metal oxide silicon field effect transistor (MOSFET). Further,since the modulator 960 includes the resistors 961 and 962, the responsetime may be minimized according to the used resistors 961 and 962.Further, the current flow may be more actively controlled by switchingon/off two transistors 963 and 964. Further, the modulator 960configured as illustrated in FIG. 9 may perform modulation through acontroller 950.

FIG. 10 is a flowchart illustrating a wireless communication method of awireless power reception device according to an embodiment of thepresent invention.

Referring to FIG. 10, the wireless power reception device receives thewireless power signal from the wireless power transmission device(S1010). In the case of receiving the wireless power signal, thewireless power transmitted from the primary coil of the wireless powertransmission device may be received by the secondary coil of thewireless power reception device.

Next, the wireless power reception device measures the strength of thereceived wireless power signal (S1020). The measured power may bealternating current (AC) or AC voltage. As one example, the wirelesspower signal may be measured by a current sensor or a voltage sensor.

Next, the wireless power reception device modulates the amplitude of thewireless power signal according to the measured strength of the wirelesspower signal (S1030). The wireless power signal may be modulated by themodulator.

As one example, in the wireless power reception device, the modulator isconfigured to be positioned between the rectifier using a plurality ofdiodes or FETs and the regulator to modulate the DC power which is theoutput of the rectifier. In this case, the modulator may include oneresistor and one or more transistors. Since the modulator includes theresistor, the response time may be minimized according to the usedresistor. Since the modulator is connected to a DC terminal of a diodebridge in series, the modulator varies a current amount in a directionin which a signal flows without an influence by the frequency to enablesmooth communication even with high power. Further, the modulator mayinclude the PNP transistor and the controller is connected to the baseterminal of the PNP transistor to control the current flow of themodulator.

As another example, the wireless power reception device is configured tobe positioned between the secondary core and the rectifier using theplurality of diodes to modulate the AC power which is the output of thesecondary core. In this case, the modulator may include two or moreresistors and two or more transistors. Since the modulator includes theresistor, the response time may be minimized according to the usedresistor. However, since the impedance varies depending on thefrequency, when the full band is used, the distortion depending on thefrequency may be caused, but the response time and frequency modulationmay be more actively controlled by using two or more resistors and twoor more transistors.

Next, the wireless power reception device performs communication withthe wireless power transmission device by using the signal with themodulated amplitude (S1040). In detail, the signal with the modulatedamplitude may be induced to the primary core of the wireless powertransmission device from the secondary core of the wireless powerreception device and the wireless power transmission device may controltransmission power by detecting the signal induced in the primary core.

According to the present invention, since the wireless power receptiondevice modulates the amplitude of the wireless power signal according tothe strength of the wireless power signal transmitted from the wirelesspower transmission device to prevent a modulated signal from beingdistorted, smooth wireless communication is available even when strongwireless power signals are transmitted.

The above description just illustrates the technical spirit of thepresent invention and various changes and modifications can be made bythose skilled in the art to which the present invention pertains withoutdeparting from an essential characteristic of the present invention.Therefore, the exemplary embodiments disclosed in the present inventionare used to not limit but describe the technical spirit of the presentinvention and the scope of the technical spirit of the present inventionis not limited by the exemplary embodiments. The scope of the presentinvention should be interpreted by the appended claims and it should beanalyzed that all technical spirit in the equivalent range thereto isintended to be embraced by the scope of the present invention.

What is claimed is:
 1. A wireless communication method by a wirelesspower reception device, the wireless communication method comprising:receiving a wireless power signal from a wireless power transmissiondevice; measuring a strength of the wireless power signal; andperforming communication with the wireless power transmission device bymodulating an amplitude of the wireless power signal in a modulatorincluded in the wireless power reception device, wherein the modulatorincludes at least one transistor that is selectively enabled based, atleast in part, on whether the strength of the wireless power signal isabove a predetermined threshold.
 2. The wireless communication method ofclaim 1, wherein the at least one transistor is any one of a metal oxidesilicon field effect transistor (MOSFET) and a bipolar junctiontransistor (BJT).
 3. The wireless communication method of claim 1,wherein the modulator is configured in a direct current (DC) terminal ofthe wireless power reception device.
 4. The wireless communicationmethod of claim 1, wherein the modulator is configured in an alternatingcurrent (AC) terminal of the wireless power reception device.
 5. Thewireless communication method of claim 1, wherein the modulator includestwo or more transistors and two or more resistors.
 6. A wireless powerreception device comprising: at least one secondary core receiving awireless power signal transmitted from a wireless power transmissiondevice; a rectifier rectifying the received wireless power signal; adetection circuit measuring a strength of the wireless power signal bymonitoring an output of the rectifier; and a controller controllingcommunication with the wireless power transmission device using amodulator to modulate an amplitude of the wireless power signal, whereinthe modulator includes at least one transistor that is selectivelyenabled based, at least in part, on whether the strength of the wirelesspower signal is above a predetermined threshold.
 7. The wireless powerreception device of claim 6, wherein the at least one transistor is anyone of a metal oxide silicon field effect transistor (MOSFET) and abipolar junction transistor (BJT).
 8. The wireless power receptiondevice of claim 6, wherein the modulator is configured in a directcurrent (DC) terminal of the wireless power reception device.
 9. Thewireless power reception device of claim 6, wherein the modulator isconfigured in an alternating current (AC) terminal of the wireless powerreception device.
 10. The wireless power reception device of claim 6,wherein the modulator includes two or more transistors and two or moreresistors.
 11. The wireless communication method of claim 1, wherein themodulator includes at least a first modulation module and a secondmodulation module, the wireless communication method further comprising:selectively enabling one of the first modulation module or the secondmodulation module based, at least in part, on whether the strength ofthe wireless power signal is above or below the predetermined threshold.12. The wireless communication method of claim 11, wherein the secondmodulation module is enabled when the strength of the wireless powersignal is above the predetermined threshold, the second modulationmodule including the at least one transistor.